Several binoculars of the folding type are known and one such type is disclosed in Australian Patent Application No. 35049184. The binoculars are comprised or a front optical element and a rear optical element connected by a resilient structure which, when compressed, changes the focus of the optical elements. The resilient structure includes an upper folded wall extending from the top of the front optical element to the top of the rear optical element and a lower folded wall extending from the bottom of the front optical element to the bottom of the rear optical element. The structure also includes side panels. The entire structure can be folded flat by folding the upper wall onto itself and by folding the lower wall onto itself such that the front optical element is disposed on top of the rear optical element.
The main difficulty in using these binoculars is that they are difficult to hold so as to maintain the front and rear optical elements at a constant spacing. The resulting view for the user is one of ever-changing focus leading to poor vision and eye strain. Further, to fold the binoculars, the various walls and panels must be folded in a particular sequence to arrive at the properly folded configuration. This is tedious. Thus the binoculars produce an unsatisfactory result and are awkward to use.
An advance over the binoculars described above is disclosed in Australian Patent Application No. 72881/87 and similarly in U.S. Pat. No. 4,443,071. A one piece blank having a series of rectangular panels including a front optical panel and a rear optical panel may be assembled to form a foldable binocular. However, these binoculars also suffer from the disadvantage that since they are made up of folded parts, they are inclined to collapse onto themselves, making them difficult to hold and operate. These binoculars also suffer from the disadvantage that they are made up of a number of panels which must be folded in proper sequence about prescribed fold lines to disassemble the binoculars. This is inconvenient.
Moreover, the binoculars disclosed in all of the above-mentioned applications are designed to be constructed from thin semi-rigid material such as cardboard which would have a short life expectancy and not withstand wet conditions. Furthermore, the binoculars in their folded state have an appreciable amount of overlapping of the panels and as such the resulting foldable binoculars could tend to be bulky and not very flat.
It is therefore an object of the present invention to provide an improved optical device which overcomes or ameliorates the above-mentioned disadvantages.